Here is the full list of all 38 Destroy All Humans! - there are Clone Carnage achievements worth 1,000 gamerscore.
Win first place in all versus challenges
In Abduction mode, find and abduct all special targets
Complete 100 online matches
Earn a three star rating on all Local Multiplayer Co-op challenges
Win one Race in Online Multiplayer
On Turnipseed Farm abduct the agent in Abduction Mode
Complete 50 online matches
Complete all versus matches
Win a match in Armageddon mode
Win a match in Abduction mode
Win a match in Rampage mode
Destroy the saucer once in Armageddon mode
Kill another player using a chicken
Complete a local match in Rampage mode
Be the first to board a UFO in Armageddon mode
In an online mutliplayer game, use Psychokinesis to stun another player
Finish an online match in Race mode
Finish an online match in Armageddon mode
Finish an online match in Abduction mode
Finish an online match in Rampage mode
Complete a local match in Race mode
Complete a local match in Armageddon mode
Complete a local match in Abduction mode
Kill another player while controlling the UFO
Fly 99.99 meters or more using the jetpack
Steal a score cube of a dead player
Drown once in water
Using Psychokinesis, catch an incoming missile
Get stunned by another player
Kill another player in Online Multiplayer while they are stunned
Stun another player in Online Multiplayer while controlling the UFO
Use the Quantum Deconstructor
Reach the drone in Race mode after another player finished the course
Revive another player in online mode
Throw the wrong object into the Beam while in abduction mode
Kill 10 enemies with one shot of the Ion Detonator
Reach a total player death count of 10 in one match
Play an online match without any upgrades